An OLED includes an anode layer, a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, an electron injection layer and a cathode layer.
In the prior art, an OLED including multiple layers is typically manufactured by using different processes. For example, a cathode layer, an electron injection layer, an electron transport layer and a light emitting layer may be formed using a vacuum evaporation method, while a hole transport layer and a hole injection layer may be formed using a solution method. In order to improve properties of an interface between two layers formed by different processes (for example, the light emitting layer and the hole transport layer), a connecting layer may also be formed between the two layers by an evaporation process. However, in such an OLED, the existence of the connecting layer may cause difficulties in balancing carriers during emission of light. Thus, in a case where the connecting layer is too thin, light emitting efficiency is reduced since carriers are quenched, and in a case where the connecting layer is too thick, a phenomenon of “unexpected emission of light” is likely to occur, that is, the OLED emits light of an undesired color (as shown in FIG. 5).